海南热区砖红壤颗粒离散元仿真模型参数标定

为获取适用于海南热区砖红壤与触土部件相互作用的离散元仿真模型参数,该文利用EDEM仿真软件中Hertz-Mindlin with JKR接触模型对海南地区砖红壤进行相关模型参数标定,首先以含水率为7.8%、实际休止角为32.35°的砖红壤为研究对象,以物理试验获取的砖红壤-砖红壤、砖红壤-触土部件间恢复系数、静摩擦系数及滚动摩擦系数为标定对象,应用Plackett-Burman设计试验筛选出对休止角有显著影响的参数:即砖红壤-砖红壤滚动摩擦系数、JKR表面能、砖红壤-28MnB5板滚动摩擦系数、砖红壤-砖红壤恢复系数。进一步以砖红壤颗粒休止角为响应值,基于Box-Behnken设计试验得到休止角与显著性参数的二阶回归模型,并以实际休止角为目标,针对显著性参数进行寻优,得到最佳组合:砖红壤-砖红壤滚动摩擦系数为0.07、砖红壤-28MnB5板滚动摩擦系数为0.24、砖红壤-砖红壤恢复系数为0.4、JKR表面能为4.31J/m^2。最后在标定的参数下进行休止角与破土阻力离散元仿真验证试验,对比计算得出仿真休止角与实测休止角相对误差为0.62%,仿真破土阻力与实测破土阻力相对误差为3.43%,并通过对比分析两次试验中破土阻力变化曲线的拟合情况,得出两曲线间的可决系数R2=0.993 9,均方根误差RMSE=0.017 7,该结果表明标定所得相关参数可用作海南热区砖红壤离散元仿真。

Parameter calibration of discrete element simulation model for latosol particles in hot areas of Hainan Province

Lateritic soil is the zonal soil of tropical rainforest or seasonal rainforest in the southernmost part of China. Compared with ordinary soil, lateritic soil has stronger expansibility, flow plasticity and water holding capacity. In the cultivation of lateritic soil, there are many problems, such as high resistance, low efficiency, and serious soil adhesion of parts touching the soil. In recent years, with the continuous improvement of agricultural mechanization level, discrete element method is gradually applied in the field of agricultural engineering. But the existing research is mainly aimed at the soil with weak viscosity, such as sandy soil, dry soil or rock soil. These research results are not suitable for the laterite soil, and there are few researches on the parameter calibration of the discrete element simulation model of laterite soil. In this paper, the the simulation contrast test of soil accumulation angle and soil breaking resistance, and calibrate the contact parameters of the discrete element model of lateritic soil have carried out with "Hertz-Mindlin with JKR" contact model in the EDEM software. The actual accumulation angle of lateritic soil with moisture content of 7.8% was measured to be 32.35 °. The recovery coefficient, static friction coefficient and rolling friction coefficient between lateritic soil, lateritic soil and contact parts were measured by design test. Seven coefficients were selected as test factors by Design-expert software and factor level was set. The accumulation angle was taken as test index and design parameter calibration test was carried out. Using Plackett-Burman Design test to determine the key factors affecting the accumulation angle of lateritic soil include recovery coefficient of lateritic soil-lateritic soil, rolling friction coefficient of lateritic soil-lateritic soil, rolling friction coefficient of lateritic soil-28MnB5 plate and surface energy. Box-Behnken test was used to regression fit the test results, and the accumulation angle regression model was obtained. The regression variance analysis of the model showed that the regression model was very significant, and the accumulation angle could be predicted according to the model. Taking the actual accumulation angle of lateritic soil as the objective value, the regression model was optimized, and the optimal values of four significant factors were obtained: lateritic soil-lateritic soil recovery coefficient 0.40, lateritic soil-lateritic soil rolling friction coefficient 0.07, lateritic soil-28MnB5 plate rolling friction coefficient 0.24, surface energy 4.31 J/m2. The simulation experiment of the accumulation angle of EDEM is designed, and the image of the simulated accumulation angle is processed by Python. The relative error between the simulated accumulation angle and the measured accumulation angle is 0.62%. The soil tank model is established to simulate the movement process of the breaking blade in the laterite soil, and the test is carried out to compare the fitting situation of the change of the breaking resistance. Comparion of soil breaking fitting resistance curve in numeral simulation and test, which shows the calibration of the parameters of the discrete element simulation model of laterite soil is accurate and reliable.